I do my case designs in Autocad. I use a seperate layer for
each different layer in the case and also a seperate layer if
I am going to use multiple laser power settings on the same
piece of acrylic. This screenshot shows the juicebox case up
in Autocad:

You can pull the CAD files for this case from the juicebox
sourceforge site. Download the cases package. In this
picture, the black lines are the 0 layer, which I am using
for the top, bottom, side plate, and buttons, since I want to
make all of those pieces out of the same stock thickness. The
pink lines are for the GFX layer (graphics), which will be
etched at low power into the pieces on the 0
layer. The pieces are mirrored so that the laser will cut the
graphics features into the back side of the 0
layer. The blue layer is for the core piece, which happens to
be called something like 4.8mm even though in this case
it is more like 9mm

Most of the design is done in Autocad, while sitting with the
electronics package and a pair of calipers. It seems to take a
couple of iterations to get all the dimensions just
right. Don't forget to take the laser kerf size into
account.

The graphics are partly done in Autocad and partly done in
Illustrator. In this design, only the text was done in
Illustrator. I wrote the text using the text function, then
stroked it with a one pixel outline. I had to play with some
options in the DFX export from illustrator to make the import
right to Autocad. I also had to delete the hatching that came
filling up the text interiors.
One really annoying feature of the cutter I use,
which utilizes I-Cut CAM software, is that it refuses to
import splines from the CAD file. Some shops may have the same
problem. To avoid sending splines into the CAM software, don't
use them when designing your part in CAD (duh!). But sometimes
you might end up with splines, like when importing stuff from
Illustrator. One solution is to:

Export from autocad to .wmf. Include a little line of
known length if you want the scale to be right when you bring
it back in.

Insert the .wmf, reassign your features to the correct
layer, rescale and reposition

This makes splines into 2D polylines.

One other feature that is required for I-cut CAM
software is a little reference mark for each layer, all in the
same place. This makes sure your different layers line up on
the cutter, which is important if you are cutting two layers
on the same piece of stock (like for the graphics).

Save the file as DXF and move on to pick the materials for
your different layers.

Selecting Stock

You will want to select a thickness for the center layer which
is as thick or thicker than your electronics package. Keep in
mind that nominal thicknesses of acrylic are not at all
accurate, so you will probably want some stock on hand in
order to make your choice. A particular brand and product seem
to be pretty consistant in thickness, but across brands and
products thickness varies by quite a bit. For instance, one
abrasion resistant brand 1/4in nominal cast acrylic I got from
McMaster Carr measures 4.9mm, while a sheet of standard cast
acrylic (also 1/4in nominal) measures 5.5mm. Kind of annoying,
but it is actually sometimes useful since the nominal sizes
only come in 1/8in incrememnts and sometimes you want a
somewhat thinner or thicker size than the nominal. All the
acutal measurements I have made indicate that the sheets are
pretty much always undersize, but by differing amounts.

For this case, I chose 1/16 nominal 1.4mm actual cast sheet
for the top and bottom plates, and 3/8 nominal 9mm actual cast
sheet for the core. I usually attach the front sheet to the
core with either epoxy or sheet adhesiv. For this case I
was going to use sheet adhesive so I peeled one side of the
protective sheet off the core stock and roll laminated some 3M
300LSE to the plastic before getting the cutter fired up.

On the cutter

I have been using a Eurolaser cutter for these project. The
cutter belongs to E Ink, and I am fortunate enough to be able
to use it for prototyping and some side projects as long as no
one can tell that I have been using it (i.e. not changing
settings, leaving trash on the table, etc.). Kind of the LNT
shop philosophy.

The Eurolaser is a medium power laser coupled to a stainless
belt drive Zund motion platform. It is a pretty nice
machine. Can't cut metal, but it has a nice big bed.

The only annoying part of the Euro is that it uses i-Cut for
CAM, and I think this program kind of stinks. Better than some
CAM tools though! Anyway, the first step is to import the DXF
file into i-Cut.

Next, we must choose a ``Tool`` for each layer in the
file. For the graphics layer, we want to choose a laser
setting which will etch through the protective film that comes
laminated to the acrylic, but not cut too much into the
plastic itself. For my laser, this is about 8% power, speed at
150mm/s max. On this exact case I was a little strong on the
laser power and it ended up cutting into the plastic a little
too much, but I was in a hurry to finish with the cutter so I
didn't go back and recut.

In general, it is a good idea to do some test cuts on scrap
stock before you cut into your juicy new sheets of
material. This is particularly true of the graphics layer
since that is the only one where we are trying to cut part way
through instead of a full through cut.

For all the through cut layers (top, back, core) I set power
to 100% and speed to 50mm/s. For the thicker stock we will
even still have to run the same cut program several times to
make it all the way through the bulk of the material.

Now turn off all the layers except graphics and put the
top/back/side stock on the machine. Run the graphics cut
once. Then without moving the material in the machine, turn
off the graphics layer and run the top/back/side program. Then
lift the pieces off the cutter and remove the rest of the
stock.

Next comes the core cutting, so throw the core stock on the
machine. If adhesive is pre-laminated to the stock, make sure
whether you should put the sheet with the adhesive facing up
or down so that it will end up on the right side to stick the
top plate on.